IP versions

Two versions of the Internet Protocol (IP) are currently in use (see IP version history for details), IP Version 4 and IP Version 6. Each version defines an IP address differently. Because of its prevalence, the generic term IP address typically still refers to the addresses defined by IPv4.

An illustration of an IP address (version 4), in both dot-decimal notation and binary.

IP version 4 addresses

Main article: IPv4#Addressing

IPv4 uses 32-bit (4-byte) addresses, which limits the address space to 4,294,967,296 (2³²) possible unique addresses. IPv4 reserves some addresses for special purposes such as private networks (~18 million addresses) or multicast addresses (~270 million addresses). This reduces the number of addresses that can be allocated to end users and, as the number of addresses available is consumed, IPv4 address exhaustion is inevitable. This foreseeable shortage was the primary motivation for developing IPv6, which is in various deployment stages around the world and is the only strategy for IPv4 replacement and continued Internet expansion.

IPv4 addresses are usually represented in dot-decimal notation (four numbers, each ranging from 0 to 255, separated by dots, e.g. 208.77.188.166). Each part represents 8 bits of the address, and is therefore called an octet. In less common cases of technical writing, IPv4 addresses may be presented in hexadecimal, octal, or binary representations. In most representations each octet is converted individually.